1. Field of Invention
This invention relates to polymer compositions, and methods of preparing them, having improved acoustic damping properties. More specifically, it relates to polymer mixtures comprising two components, a soft polymer component and a hard polymer component, which are intimately mixed on a molecular scale, such mixtures being referred to as "interpenetrating polymer networks."
2. Description of the Prior Art
Interpenetrating polymer networks having improved acoustic damping characteristics are known to the art.
U.S. Pat. No. 3,833,404 discloses interpenetrating polymer networks to be used for surface layers or coatings for damping vibrations or noise-emitting surfaces. The material consists of poly ethylacrylate cross-linked with a polyglycol dimethacrylate, and polystyrene cross-linked with divinylbenzene.
U.S. Pat. No. 4,302,553 discloses a number of interpenetrating polymer networks having improved tensile strength and swelling properties in presence of solvents, including combinations of polyurethanes with polyacrylates, polyepoxides, polyesters, styrene-butadiene polymers and polydimethyl siloxanes.
U.S. Pat. No. 4,342,793 describes curable resin compositions for protective surface coatings consisting of interpenetrating polymer networks prepared from saturated polyols, acrylate and methacrylate esters, and polyisocyanates, by radiation and thermal curing.
U.S. Pat. Nos. 4,618,658 and 4,719,268 describe polymer modified epoxy resin compositions comprising the copolymerization product of an epoxy resin wherein part of the epoxide groups have been modified to provide polymerizable ethylenic unsaturation; vinyl-terminated urethane oligomer; and a polymerizable ethylenically unsaturated compound such as styrene or an acrylate ester.
U.S. Pat. No. 4,742,128 discloses compositions for molded products consisting of an interpenetrating polymer network comprising a polyamide and a polyurethane.
U.S. Pat. No. 4,752,624 describes an interpenetrating polymer network for selective permeation membranes comprising a hydrophilic and a hydrophobic polymer component. The hydrophylic component is made from hexamethylene diisocyanate and poly ethylene ether glycol, and cross-linked with trimethylolpropane. The hydrophobic polymer component is polystyrene cross-linked with divinylbenzene.
U.S. Pat. No. 4,766,183 discloses a heat-curable composition comprising a urethane/epoxy/silicone interpenetrating polymer network.
U.S. Pat. No. 4,824,919 describes vinyl ester/styrene composition flexibilized by the addition of a small amount of polyurethane.
U.S. Pat. No. 4,902,737 discloses a resin having improved impact properties comprising an aromatic carbonate resin/polyester blend modified by the addition of a first elastomeric phase of cross-linked polyacrylate, and a second phase of cross-linked styrene/acrylonitrile.
U.S. Pat. No. 4,923,934 discloses a coating having improved flexibility, resistance to chemical attack and corrosion, and adhesion, consisting of an interpenetrating polymer network including a blocked urethane prepolymer, a polyol, an epoxy resin, and an epoxy catalyst.
U.S. Pat. No. 4,957,981 describes a polymeric material to be used for optical products such as lenses, goggles, and watch covers comprising an interpenetrating polymer network of a polyol(allylcarbonate) and an epoxy resin.
U.S. Pat. No. 4,992,506 provides a molding composition having improved flexural modulus and softness (lower modulus) comprising an interpenetrating polymer network of one or more thermoplastic copolyetheresters, one or more aromatic thermoplastic polyesters, a rubbery polymer comprising cross-linked (meth)acrylate, and an interpenetrating cross-linked styrene resin; and, optionally, a mineral filler.